Gonna use this "old" topic, because pictures and schematics already exist here. I have two of these units - one works 100% fine, the second one has some burned shunts, resistors and shorted caps. Shunts are already replaced as are the caps (except the filtercaps which seems to be fine), meter does "work" in most ranges perfectly fine. While checking parameters from the service manual, the manual wishes for 0 Volts between "LO" (shorted together with HI) and RX2 Input. The fully working G-1001.500 only shows about 4-10 mV at worst, but the second unit shows 0,5 V from start slowly rising to about 0,8 and sometimes close to 1 Volt.
The basics don't seem to be affected ... 1 Volt DC is 1,000 VDC, 1k Ohm precision resistor shows as 1k, 1 mA is 1 mA and 1 VAC (1kHz/Sine) shows as 1 VAC in AC-Mode. So i guess it kinda works, but still the book wants 0 Volts between LO/HI and RX2 Input-Terminals. R287 does change the measured voltage between LO and Rx2 (as stated in the manual) but the "Zero @display" will be way off scale. Right now display is perfectly zeroed and any change with R287 (which should be used to lower the voltage between LO/HI and Rx2 throws of the ZERO). I wonder if this is "from factory" and they just "compensated" for it further down the line.
So in short: If i change R287, R276 or R277 i could achieve "0 Volts" between Hi/Lo and Rx2 Inputs but the Zero will be waaaaaay off.
Best wishes!
By the way, my unit has original Nippon-Chemicon filtercaps and HP-parts build in and it seems this was done "from factory" even with sanctions in place in the old days.